Semiconductor device

ABSTRACT

A semiconductor device according to embodiments includes a normally-off transistor having a first electrode, a second electrode, and a first control electrode, a normally-on transistor having a third electrode electrically connected to the second electrode, a fourth electrode, and a second control electrode, a first element having a first end portion electrically connected to the first control electrode and a second end portion electrically connected to the first electrode, and the first element including a first capacitance component; and, a second element having a third end portion electrically connected to the first control electrode and the first end portion and a fourth end portion, and the second element including a second capacitance component, wherein, when a threshold voltage of the normally-off transistor is denoted by V th , a maximum rated gate voltage of the normally-off transistor is denoted by V g_max , a voltage of the fourth end portion is denoted by V g_on , the first capacitance component is denoted by C a , and the second capacitance component is denoted by C b , V th &lt;(C b /(C a +C b ))V g_on &lt;V g_max .

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 16/745,457, filed on Jan. 17, 2020, which is based upon and claimsthe benefit of priority from Japanese Patent Application No.2019-168195, filed on Sep. 17, 2019, the entire contents of which areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to Semiconductor Device.

BACKGROUND

As a material for next-generation power semiconductor devices, agroup-III nitride, for example, a GaN (gallium nitride) -basedsemiconductor has been expected. The GaN-based semiconductor has a largebandgap in comparison with Si (silicon). For this reason, in comparisonwith an Si (silicon) semiconductor device, by using a GaN-basedsemiconductor device, a power semiconductor device with a small size anda high breakdown voltage can be implemented. In addition, accordingly, aparasitic capacitance can be reduced, and thus, a power semiconductordevice with high-speed driving can be implemented.

Generally, a high electron mobility transistor (HEMT) structure using atwo-dimensional electron gas (2DEG) as carriers is applied to aGaN-based transistor. Atypical HEMT is a normally-on transistor whichbecomes conductive even when no voltage is applied to the gate. For thisreason, there is a problem in that it is difficult to implement anormally-off transistor which does not become conductive if no voltageis applied to the gate.

In such a power supply circuit for dealing with a large power of severalhundred volts to one thousand volts, the normally-off operation isrequired in terms of emphasis on safety. Therefore, a circuitconfiguration for implementing the normally-off operation by connectinga normally-on GaN-based transistor and a normally-off Si transistor hasbeen proposed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a power conversion system of a firstembodiment;

FIG. 2 is a circuit diagram of a semiconductor device of the firstembodiment;

FIGS. 3A to 3C are schematic diagrams illustrating examples of V_(g_on);

FIG. 4 is a circuit diagram of a semiconductor device as a comparativeform of the first embodiment;

FIG. 5 is a circuit diagram of a semiconductor device of a secondembodiment; and

FIG. 6 is a circuit diagram of a semi conductor device of a thirdembodiment.

DETAILED DESCRIPTION

A semiconductor device of an embodiment includes a normally-offtransistor having a first electrode, a second electrode, and a firstcontrol electrode; a normally-on transistor having a third electrodeelectrically connected to the second electrode, a fourth electrode, anda second control electrode; a first element having a first end portionelectrically connected to the first control electrode and a second endportion electrically connected to the first electrode, and the firstelement including a first capacitance component; and a second elementhaving a third end portion electrically connected to the first controlelectrode and the first end portion and a fourth end portion, and thesecond element including a second capacitance component, wherein, when athreshold voltage of the normally-off transistor is denoted by V_(th), amaximum rated gate voltage of the normally-off transistor is denoted byV_(g_max), a voltage of the fourth end portion is denoted by V_(g_on),the first capacitance component is denoted by C_(a), and the secondcapacitance component is denoted by C_(b),V_(th)<(C_(b)/(C_(a)+C_(b)))V_(g_on)<V_(g_max).

Hereinafter, embodiments will be described with reference to theaccompanying drawings. In addition, in the following description, insome cases, the same or similar members are denoted by the samereference numerals. In addition, in some cases, description of theonce-described member or the like is omitted as appropriate.

In addition, in this specification, a semiconductor device is a conceptincluding a power module obtained by incorporating a plurality ofelements such as discrete semiconductors, an intelligent power moduleobtained by incorporating a drive circuit for driving a plurality ofelements such as discrete semiconductors or a self protection functioninto the plurality of elements, or an entire system including the powermodule or the intelligent power module.

In addition, in this specification, a “GaN-based semiconductor” is ageneric name of semiconductors having GaN (gallium nitride), AlN(aluminum nitride), InN (indium nitride), and an intermediatecomposition thereof.

(First Embodiment)

A semiconductor device of this embodiment includes a normally-offtransistor having a first electrode, a second electrode, and a firstcontrol electrode; a normally-on transistor having a third electrodeelectrically connected to the second electrode, a fourth electrode, anda second control electrode; a first element having a first end portionelectrically connected to the first control electrode and a second endportion electrically connected to the first electrode, and the firstelement including a first capacitance component; and a second elementhaving a third end portion electrically connected to the first controlelectrode and the first end portion and a fourth end portion, and thesecond element including a second capacitance component, wherein, when athreshold voltage of the normally-off transistor is denoted by V_(th), amaximum rated gate voltage of the normally-off transistor is denoted byV_(g_max), a voltage of the fourth end portion is denoted by V_(g_on),the first capacitance component is denoted by C_(a), and the secondcapacitance component is denoted by C_(b),V_(th)<(C_(b)/(C_(a)+C_(b)))V_(g_on)<V_(g_max).

The first element is a first capacitor having a fifth end port ion and asixth end portion, and includes a first capacitance. The first endportion is the fifth end portion, the second end portion is the sixthend portion, and the first capacitance component is the firstcapacitance.

FIG. 1 is a schematic diagram of a power conversion system 900 of thisembodiment.

The power conversion system 900 includes a power conversion device 800and a motor 810.

The power conversion device 800 includes transistors 200 a, 200 b, 200c, 200 d, 200 e, and 200 f, a DC power supply 300, a converter 400, anda smoothing capacitor 500. In addition, as described below, thetransistors 200 a, 200 b, 200 c, 200 d, 200 e, and 200 f may alsoinclude a plurality of transistors and the other elements.

The DC power supply 300 outputs a DC voltage. The converter 400 is aDC-DC converter and converts the DC voltage output by the DC powersupply 300 to other DC voltage. The smoothing capacitor 500 smooths thevoltage output by the converter 400.

Each of the transistors 200 a, 200 b, 200 c, 200 d, 200 e, and 200 fincludes a semiconductor device 100 described later. The DC voltagesmoothed by the smoothing capacitor 500 is converted into an AC voltageby the transistors 200 a, 200 b, 200 c, 200 d, 200 e, and 200 f.

For example, the transistor 200 a has a first transistor electrode 202and a second transistor electrode 204. The transistor 200 b has a thirdtransistor electrode 206 and a fourth transistor electrode 208. Thetransistor 200 a and the transistor 200 b are electrically connected toeach other by electrically connecting the first transistor electrode 202and the fourth transistor electrode 208.

Similarly, the transistor 200 c and transistor 200 d are electricallyconnected to each other, and the transistor 200 e and the transistor 200f are electrically connected to each other.

The motor 810 has coils 810 u, 810 v, and 810 w. Ends of the coils 810u, 810 w, and 810 v are electrically connected to each other at aneutral point 820. The other end of the coil 810 u is electricallyconnected between the transistor 200 a and the transistor 200 b. Theother end of the coil 810 v is electrically connected between thetransistor 200 c and transistor 200 d. in addition, the other end of thecoil 810 w is electrically connected between the transistor 200 e andthe transistor 200 f.

In addition, the ground in the power conversion device 800 of thisembodiment may be electrically connected, for example, between theplurality of smoothing capacitors 500 provided. In addition, the groundin the power conversion device 800 may be electrically connected to, forexample, a wire where the transistor 200 b, the transistor 200 d, andthe transistor 200 f are electrically connected to each other.

FIG. 2 is a circuit diagram of the semiconductor device 100 of thisembodiment. The semiconductor device 100 of this embodiment is a powermodule having a rated voltage of, for example, 600 V and 1200 V.

The semiconductor device 100 includes a normally-off transistor 10, anormally-on transistor: 20, a first element 1, a second element 5, afirst diode 80, a second diode 90, a third capacitor 85, a third diode70, a resistor 75, a gate drive circuit 96, and a signal source 97.

The normally-off transistor 10 has a first electrode 11, a secondelectrode 12, and a first control electrode 13.

The normally-off transistor 10 is a transistor in which a drain currentdoes not flow in a case where a voltage is not input to the gate. Thenormally-off transistor 10 is, for example, an n-type metal oxidesemiconductor field effect transistor (MOSFET) using an Si (silicon)semiconductor. For example, the first electrode 11 is the sourceelectrode, the second electrode 12 is the drain electrode, and the firstcontrol electrode 13 is the gate electrode. However, the normally-offtransistor 10 is not limited thereto. For example, the normally-offtransistor 10 may be a p-type MOSFET.

C_(gs1) is a parasitic capacitance of the normally-off transistor 10. Itis preferable that the first capacitance component is 10 times or morelarger than C_(gs1) in order to input a stable voltage that isindependent of the parasitic capacitance C_(gs1) of the normally-offtransistor 10 between the first control electrode 13 and the firstelectrode 11. In addition, the normally-off transistor 10 includes aparasitic body diode (not illustrated).

The breakdown voltage of the normally-off transistor 10 is, for example,10 V or more and 30 V or less.

The normally-on transistor 20 has a third electrode 21, a fourthelectrode 22, and a second control electrode 23. The third electrode 21is electrically connected to the second electrode 12. In addition, thesecond terminal 102 is electrically connected to the fourth electrode22.

The normally-on transistor 20 is a transistor in which a drain currentflows even in a case where a voltage is not input to the gate. Thenormally-on transistor 20 is, for example, an HEMT using a GaN-basedsemiconductor. For example, the third electrode 21 is the sourceelectrode, the fourth electrode 22 is the drain electrode, and thesecond control electrode 23 is the gate electrode.

The breakdown voltage of the normally-on transistor 20 is higher thanthe breakdown voltage of the normally-off transistor 10. The breakdownvoltage of the normally-on transistor 20 is, for example, 600 V or moreand 1200 V or less.

C_(gs2) is a parasitic capacitance of the normally-on transistor 20.

The first element 1 has a first end portion 2 and a second end portion3. The first end portion 2 is electrically connected to the firstcontrol electrode 13. The second end portion 3 is electrically connectedto the first electrode 11.

The first element 1 in this embodiment is a first capacitor 30. Thefirst capacitor 30 has a fifth end portion 31 and a sixth end portion32. In addition, the first capacitor 30 includes a first capacitance C₁.The fifth end portion 31 is the first end portion 2, the sixth endportion 32 is the second end portion 3, and the first capacitancecomponent C₁ is the first capacitance C₁. In addition, the firstterminal 101 is electrically connected to the sixth end portion 32 andthe first electrode 11.

The second element 5 has a third end portion 6 and a fourth end portion7. The third end portion 6 is electrically connected to the firstcontrol electrode 13 and the first end portion 2.

The second element 5 in this embodiment is a second capacitor 40. Thesecond capacitor 40 has a seventh end portion 41 and an eighth endportion 42. In addition, the second capacitor 40 includes a secondcapacitance C₂. The seventh end portion 41 is the third end portion 6,the eighth end portion 42 is the fourth end portion 7, and the secondcapacitance component C_(b) is the second capacitance C₂.

The semiconductor device 100 of this embodiment implements anormally-off operation by electrically connecting the normally-offtransistor 10 and the normally-on transistor 20 in series. For example,in a case where the semiconductor device 100 is used in the transistor200 b (FIG. 1), the third transistor electrode 206 is electricallyconnected to the first electrode 11 and the sixth end portion 32 via thefirst terminal 101, and the fourth transistor electrode 208 iselectrically connected to the fourth electrode 22 via the secondterminal 102.

The third diode 70 has an anode 71 (an example of a fifth anode) and acathode 72 (an example of a fifth cathode). The cathode 72 iselectrically connected to the fourth end portion 7 (the eighth endportion 42).

The resistor 75 has an end portion 76 (an example of an eleventh endportion) and an end portion 77 (an example of a twelfth end portion),The end portion 76 is electrically connected to the fourth end portion 7(the eighth end portion 42) and the cathode 72. The end portion 77 iselectrically connected to the anode 71. The resistor 75 is provided inparallel with the third diode 70.

The first diode 80 has an anode 81 (an example of a third anode) and acathode 82 (an example of a third cathode). The anode 81 is electricallyconnected to the second control electrode 23. The cathode 82 iselectrically connected to the second electrode 12 (third electrode 21).

The third capacitor 85 has an end portion 86 (an example of a ninth endportion) and an end portion 87 (an example of a tenth end portion). Theend portion 86 is electrically connected to the second control electrode23 and the anode 81.

The second diode 90 has an anode 91 (an example of a fourth anode) and acathode 92 (an example of a fourth cathode). The anode 91 iselectrically connected to the second control electrode 23, the anode 81,and the end portion 86. The cathode 92 is electrically connected to theend portion 87. The second diode 90 is provided in parallel with thethird capacitor 85.

The first diode 80, the second diode 90, and the third diode 70 arepreferably Schottky barrier diodes having a high response speed. Inaddition, the first diode 80, the second diode 90, and the third diode70 may be PN junction diodes, and even in the case, the diodes can bepreferably used.

The first capacitor 30, the second capacitor 40, and third capacitor 85are preferably ceramic capacitors. This is because a ceramic capacitoris excellent in frequency characteristic. However, the first capacitor30, the second capacitor 40, and the third capacitor 85 may be otherfilm capacitors, aluminum electrolytic capacitors, tantalum electrolyticcapacitors, or the like, and even in the case, the capacitors can bepreferably used.

The signal source 97 outputs, for example, a signal of a square wave orthe like.

The gate drive circuit 96 is connected to the signal source 97, theanode 71, the end portion 77, the end portion 87, and the cathode 92. Inaddition, the gate drive circuit 96 is electrically connected to thesecond control electrode 23 via the second diode 90 and is electricallyconnected to the first control electrode 13 via the third diode 70 orthe second element 5. The gate drive circuit 96 outputs a signal fordriving the normally-off transistor 10 and the normally-on transistor 20on the basis of the signal output from the signal source 97.

The gate drive circuit 96 is an IC obtained by incorporating a pluralityof elements into one chip or an electronic circuit board on which aplurality of electronic components are arranged.

When a threshold voltage of the normally-off transistor 10 is denoted byV_(th), a maximum rated gate voltage of the normally-on transistor 20 isdenoted by V_(g_max), a voltage of the fourth end portion 7 is denotedby V_(g_on), the first capacitance component is denoted by C_(a), andthe second capacitance component is denoted by C_(b),V_(th)<(C_(b)(C_(a)+C_(b)))V_(g_on)<V_(max). In addition, if the voltagedrop across the third diode 70 and the resistor 75 is ignored, thevoltage V_(g_on), the fourth end portion 7 can be considered to be equalto the output voltage of the gate drive circuit 96. Hereinafter, theoutput voltage of the gate drive circuit 96 is described to be V_(g_on).In addition, V_(g_on) is the voltage measured by setting the voltage ofthe first terminal 101 or the voltage of the first electrode 11 as areference. Herein, the phrase “setting the voltage . . . as a reference”denotes, for example, “setting the voltage . . . to 0 V”.

FIGS. 3A to 3C are schematic diagrams illustrating examples of V_(g_on).FIG. 3A illustrates a case where the output voltage of the gate drivecircuit 96 is a square wave where 0 output during the time t₁ andV_(g_on) output during the time t₂ repeat. FIG. 3B illustrates a casewhere the output voltage of the gate drive circuit 96 is a square wavewhere V₁ output during the time t₁ and a sum of V₁ and V₂ output duringthe time t₂ repeat. In the case of FIG. 3B,V_(g_on)=V₁+V₂(V_(g_on)=|V₁|+|V₂|). FIG. 3C illustrates a case where anegative voltage is output during the time t₁. In the case of FIG. 3C,V_(g_on)=|V₂|−|V₁|. Thus, the output voltage of the gate drive circuit96 is a time varying voltage. Then, for example, the maximum voltage outof the output voltages of the gate drive circuit 96 is V_(g_on). Inaddition, although t₁=t₂ is illustrated in FIGS. 3A to 3C, t₁ and t₂ maybe different. In addition, the time varying manner of the output voltageof the gate drive circuit 96 is not limited to those illustrated inFIGS. 3A to 3C. In addition, can be easily measured by using acommercially available oscilloscope or the like.

Next, operations of the semiconductor device 100 of this embodiment aredescribed.

For example, a square wave which reciprocates between 0 V and V_(g_on)as illustrated in FIG. 3A is output by using the signal source 97 andthe gate drive circuit 96.

When V_(g_on) is output from the gate drive circuit 96, a current flowsfrom the third capacitor 85 via the first diode 80. A voltagecorresponding to a forward voltage V_(F) of the first diode 80 is inputbetween the second control electrode 23 and the third electrode 21. As aresult, the normally-on transistor 20 is turned “on”. On the other hand,when 0 V is output from the gate drive circuit, 96, a current flowsthrough a parasitic capacitance to the third capacitor 85. A negativevoltage (V_(F)−V_(g_on)) corresponding to the difference between V_(F)and V_(g_on) is input between the second control electrode 23 and thethird electrode 21. Thus, it is possible to turn “off” the normally-ontransistor 20.

In addition, when is output from the gate drive circuit 96, a voltageinput between the first control electrode 13 and the first electrode 11is (C_(b)(C_(a)+C_(b)))V_(g_on). Thus, ifV_(th)<(C_(b)/(C_(a)+C_(b)))V_(g_on), the normally-off transistor 10 isturned. “on”. In addition, when 0 V is output from the gate drivecircuit 96, the normally-off transistor 10 is turned “off”.

Herein, when the semiconductor device 100 is transitioned from “off” to“on”, it is preferable that the normally-off transistor 10 is turned“on” earlier than the normally-on transistor 20. This is because, if thenormally-on transistor 20 is turned “on” earlier, a high voltage isapplied to a connection portion between the second electrode 12 and thethird electrode 21, and thus, there is a concern that thecharacteristics of the normally-off transistor 10 having a low breakdownvoltage are deteriorated.

In the semiconductor device 100 of this embodiment, when thesemiconductor device 100 is to be transitioned from the “off” state tothe “on” state, the current output from the gate drive circuit 96 flowsthrough the third diode 70. For this reason, the charging of the firstcontrol electrode 13 is not affected by the resistor 75. Accordingly,the first control electrode 13 can be rapidly charged. Thus, when thesemiconductor device 100 is transitioned from the “off” state to the“on” state, it is possible to reliably turn “on” the normally-offtransistor 10 earlier than the normally-on transistor 20.

In addition, by providing the resistor 75, the timing of turning “off”the normally-off transistor 10 can be delayed by a desired time from thetiming of turning “off” the normally-on transistor 20.

In addition, a case is considered where 0 V is output by the signalsource 97 and the gate drive circuit 96, and thus, both the normally-offtransistor 10 and the normally-on transistor 20 are turned “off”. If ahigh voltage is applied to the fourth electrode 22, the voltage of thethird electrode 21 becomes high. At this time, there is a concern thatthe “off” state of the normally-on transistor 20 may not be maintained.For this reason, by providing the second diode 90, the gate drivecircuit 96 and the second control electrode 23 are short-circuited, sothat the “off” state of the normally-on transistor 20 is maintained.

Next, functions and effects of the semiconductor device 100 of thisembodiment are described.

FIG. 4 is a circuit diagram of a semiconductor device 1000 according toa comparative form of this embodiment. The semiconductor device 1000 isdifferent from the semiconductor device 100 in that the first element 1and the second element 5 are not provided.

For example, in a case where the normally-on transistor 20 is an HEMIusing a GaN (gallium nitride)-based semiconductor, in order to turn“off” the normally-on transistor 20, it is preferable that the absolutevalue of the negative voltage (V_(F)−V_(g_on)) is, for example, about 7V or more and 15 V or less. Herein, since V_(F) is generally as small asabout 1 V, it is preferable that V_(g_on) is, for example, about 8 V ormore and 16 V or less.

However, in a case where such V_(g_on) is input between the firstcontrol electrode 13 and the first electrode 11, since is too high,there is a concern that the normally-off transistor 10 is destroyed.

In order to suppress the destruction of the normally-off transistor 10,it is considered that the signal source and the gate drive circuit areprovided to each of the normally-off transistor 10 and the normally-ontransistor 20. However, since the two signal sources and the two gatedrive circuits are provided in one semiconductor device 100, there is aproblem in that the structure becomes complicated.

In addition, in order to simplify the structure, it is considered thatthe second control electrode 23 is electrically connected to the firstelectrode 11. However, in this case, there is a problem in that it isdifficult to control on and off of the normally-on transistor 20.

The semiconductor device 100 of this embodiment includes the firstelement 1 having the first end portion 2 electrically connected to thefirst control electrode 13 and the second end portion 3 electricallyconnected to the first electrode 11 and including a first capacitancecomponent. In addition, the semiconductor device 100 of this embodimentincludes the second element 5 having the third end portion 6electrically connected to the first control electrode 13 and the firstend portion 2 and the fourth end portion 7, and the second element 5includes a second capacitance component.

The voltage V_(g_on) output from the gate drive circuit 96 is divided bythe first capacitance component and the second capacitance component tobe input between the first control electrode 13 and the first electrode11. That is, since the voltage lower than V_(g_on) is input between thefirst control electrode 13 and the first electrode 11, a concern thatthe normally-off transistor 10 is destroyed is suppressed. For thisreason, it is possible to provide a semiconductor device having a simplestructure.

In addition, when a threshold voltage of the normally-off transistor 10is denoted by V_(th), a maximum rated gate voltage of the normally-offtransistor 10 is denoted by V_(g_max), a voltage of the fourth endportion 7 is denoted by V_(g_on), the first capacitance component isdenoted by C_(a), and the second capacitance component is denoted byC_(b), it is preferable thatV_(th)<(C_(b)/C_(a)+C_(b)))V_(g_on)<V_(g_max). Herein,(C_(b)/(C_(a)+C_(b)) is a voltage obtained by dividing the voltageV_(g_on) by the first capacitance component and the second capacitancecomponent. In order to turn “on” the normally-off transistor 10, it ispreferable that V_(th)<(C_(b)/(C_(a)+C_(b)) . In addition, in order notto destroy the normally-off transistor 10, it is preferable that(C_(b)/(C_(a)+C_(b)))V_(g_on)<V_(g_max).

According to the semiconductor device of this embodiment, it is possibleto provide a semiconductor device having a simple structure.

(Second Embodiment)

In a semiconductor device of this embodiment, the first element 1 is afirst Zener diode 50 having a first anode 51 and a first cathode 52 andincluding a first junction capacitance C_(x). The first end portion 2 isthe first cathode 52, the second end portion 3 is the first anode 51,and the first capacitance component C_(a) is the first junctioncapacitance C_(x). In addition, the second element 5 is a second Zenerdiode 60 having a second anode 61 and a second cathode 62 and includinga second junction capacitance C_(y), the third end portion 6 is thesecond anode 61, the fourth end portion 7 is the second cathode 62, andthe second capacitance component C_(b) is the second junctioncapacitance C_(y).

Herein, description of contents overlapped with the first embodiment isomitted.

FIG. 5 is a circuit diagram of a semiconductor device 110 of thisembodiment.

The first Zener diode 50 has a function of allowing the chargesaccumulated in the first control electrode 13 to escape from the firstcathode 52 to the first anode 51 when the voltage of the first controlelectrode 13 becomes too high. In addition, the first junctioncapacitance C_(x) of the first Zener diode 50 is used as the firstcapacitance component C.

When the first breakdown voltage of the first Zener diode 50 is denotedby V_(z)(D₁) , it is preferable that V_(z)(D₁)<V_(g_max). IfV_(z)(D₁)≥V_(g_max), a voltage of V_(g_max) or more is input between thefirst control electrode 13 and the first electrode 11, and thus, thereis a concern that the normally-off transistor 10 is destroyed.

In a case where the voltage input between the first control electrode 13and the first electrode 11 is too low, the second Zener diode 60 has afunction of increasing the voltage input between the first controlelectrode 13 and the first electrode 11 by the voltage output from thegate drive circuit 96. In addition, the second junction capacitanceC_(y) of the second Zener diode 60 is used as the second capacitancecomponent C_(b).

When the second breakdown voltage of the second Zener diode 60 isdenoted by V_(z)(D₂) , it is preferable that V_(z)(D₂)<V_(g_on)−V_(th).This means that, since the voltage input between the first controlelectrode 13 and the first electrode 11 corresponding to the amount ofthe second breakdown voltage of the second Zener diode 60 is lowered, inorder to operate the normally-off transistor 10, it is preferable toincrease the voltage V_(g_on) output from the gate drive circuit 96 soas to compensate for this.

In other words, the range of voltage input between the first controlelectrode 13 and the first electrode 11 is limited by the first Zenerdiode 50 and the second Zener diode 60. For this reason, the operationof the normally-off transistor 10 is stabilized, and thus, theoccurrence of destruction is further suppressed.

According to the semiconductor device of this embodiment, it is possibleto provide a semiconductor device having a simple structure.

(Third Embodiment)

A third embodiment is different from the first embodiment in that, in asemiconductor device of this embodiment, the first Zener diode 50 isconnected in parallel with the first capacitor 30, and the second Zenerdiode 60 is connected in parallel with the second capacitor 40.

Herein, description of contents overlapped with the first and secondembodiments will be omitted.

FIG. 6 is a circuit diagram of a semiconductor device 120 of thisembodiment.

The first cathode 52 of the first Zener diode 50 is electricallyconnected to the fifth end portion 31 of the first capacitor 30. Thefirst anode 51 of the first Zener diode 50 is electrically connected tothe sixth end portion 32 of the first capacitor 30. The first Zenerdiode 50 is connected in parallel with the first capacitor 30.

In addition, the second anode 61 of the second Zener diode 60 iselectrically connected to the seventh end portion 41 of the secondcapacitor 40. The second cathode 62 of the second

Zener diode 60 is electrically connected to the eighth end portion 42 ofthe second capacitor 40. The second Zener diode 60 is connected inparallel with the second capacitor 40.

The first capacitance component C_(a) and the second capacitancecomponent C_(b) are preferably the first capacitance C₁ of the firstcapacitor 30 and the second capacitance C₂ of the second capacitor 40,respectively. There is a possibility that the first junction capacitanceC_(x) of the first Zener diode 50 and the second junction capacitanceC_(y) of the second Zener diode 60 are changed by an applied voltage.For this reason, the voltage V_(g_on) output from the gate drive circuit96 can be easily estimated with high accuracy by using the firstcapacitance C₁ of the first capacitor 30 and the second capacitance C₂of the second capacitor 40.

In addition, in order to estimate the voltage V_(g_on) with higheraccuracy, it is preferable that the first capacitance component C, isset to a combined capacitance (C₁C_(x)/ (C₁+C_(x))) in a case where thefirst capacitance C₁ of the first capacitor 30 and the first junctioncapacitance C_(x) of the first Zener diode 50 are connected in parallel.In addition, it is preferable that the second capacitance componentC_(b) is set to a combined capacitance (C₂C_(y)/(C₂+C_(y))) in a casewhere the second capacitance C₂ of the second capacitor 40 and thesecond junction capacitance C_(y) of the second Zener diode 60 areconnected in parallel.

According to the semiconductor device of this embodiment, it is possibleto provide a semiconductor device having a simple structure.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, SEMICONDUCTOR DEVICE described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the devices andmethods described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the inventions.

What is claimed is:
 1. A semiconductor device comprising: a normally-offtransistor having a first electrode, a second electrode, and a firstcontrol electrode; a normally-on transistor having a third electrodeelectrically connected to the second electrode, a fourth electrode, anda second control electrode; a first element having a first end portionelectrically connected to the first control electrode and a second endportion electrically connected to the first electrode, and the firstelement including a first capacitance component; and a second elementhaving a third end portion electrically connected to the first controlelectrode and the first end portion and a fourth end portion, and thesecond element including a second capacitance component.
 2. Thesemiconductor device according to claim 1, wherein the first element isa first Zener diode having a first anode and a first cathode, and thefirst element including a first junction capacitance, and wherein thefirst end portion is the first cathode, the second end portion is thefirst anode, and the first capacitance component is the first junctioncapacitance.
 3. The semiconductor device according to claim 1, whereinthe first element is a first capacitor having a fifth end portion and asixth end portion, and the first element includes a first capacitance,and wherein the first end portion is the fifth end portion, the secondend portion is the sixth end portion, and the first capacitancecomponent is the first capacitance.
 4. The semiconductor deviceaccording to claim 3, further comprising a first Zener diode having afirst cathode electrically connected to the first end portion and afirst anode electrically connected to the second end portion, and thefirst Zener diode being connected in parallel with the first capacitor.5. The semiconductor device according to claim 2, wherein, when thefirst breakdown voltage of the first Zener diode is denoted by V_(z)(D₁), and a maximum rated gate voltage of the normally-off transistor isdenoted by V_(g_max), V_(z)(D₁)<V_(g_max).
 6. The semiconductor deviceaccording to claim 1, wherein the second element is a second Zener diodehaving a second anode and a second cathode, and the second elementincluding a second junction capacitance, and wherein the third endportion is the second anode, the fourth end portion is the secondcathode, and the second capacitance component is the second junctioncapacitance.
 7. The semiconductor device according to claim 1, whereinthe second element is a second capacitor having a seventh end portionand an eighth end portion, and the second element includes a secondcapacitance, and wherein the third end portion is the seventh endportion, the fourth end portion is the eighth end portion, and thesecond capacitance component is the second capacitance.
 8. Thesemiconductor device according to claim 7, further comprising a secondZener diode having a second anode electrically connected to the thirdend portion and a second cathode electrically connected to the fourthend portion, and the second Zener diode being connected in parallel withthe second capacitor.
 9. The semiconductor device according to claim 6,wherein, when the second breakdown voltage of the second Zener diode isdenoted by V_(z)(D₂), a voltage of the fourth end portion is denoted byand a threshold voltage of the normally-off transistor is denoted byV_(th),V_(z)(D₂)<V_(g_on)−V_(th).
 10. The semiconductor device according toclaim 1, further comprising a first diode having a third anodeelectrically connected to the second control electrode and a thirdcathode electrically connected to the third electrode.
 11. Thesemiconductor device according to claim 1, further comprising: a seconddiode having a fourth anode electrically connected to the second controlelectrode and a fourth cathode; and a third capacitor having a ninth endportion electrically connected to the fourth anode and a tenth endportion electrically connected to the fourth cathode, and the thirdcapacitor being connected in parallel with the second diode.
 12. Thesemiconductor device according to claim 1, further comprising: a thirddiode having a fifth cathode electrically connected to the fourth endportion and a fifth anode; and a resistor having an eleventh end portionelectrically connected to the fifth cathode and a twelfth end portionelectrically connected to the fifth anode, and the resistor beingconnected in parallel with the third diode.
 13. The semiconductor deviceaccording to claim 1, further comprising a gate drive circuitelectrically connected to the first control electrode and the secondcontrol electrode.
 14. The semiconductor device according to claim 1,wherein, when a threshold voltage of the normally-off transistor isdenoted by V_(th), a maximum rated gate voltage of the normally-offtransistor is denoted by V_(g_max), a voltage of the fourth end portionis denoted by V_(g_on), the first capacitance component is denoted byC_(a), and the second capacitance component is denoted by C_(b),V_(th)<(C_(b)/(C_(a)+C_(v)))V_(g_on)<V_(g_max).